(a) Field of the Invention
The invention relates to an electronic device, particularly to a road side data exchange device.
(b) Description of the Related Art
The global positioning system (GPS) has been extensively used in daily life and the most commonly seen application is a vehicular positioning device for planning and navigating the destination and promoting traffic safety, etc. However, GPS cannot have positioning 100% precisely yet and have an error of about 10˜15 meters without using calibration.
In order to perform more precisely satellite-based positioning, a calibration signal from a differential GPS should be received to do calibration. Reference stations are set and are used to acquire calibration values of the GPS positions so as to effectively calibrate errors caused by satellite electronic clocks, ephemeris, ionosphere and troposphere. However, the error caused by multipath still cannot be effectively improved. When a user is far away from the reference station, the differences of the terrain, weather or ionosphere data at which the user and the reference station are located are the major factors to cause the calibration result away from the expected value. Besides, the cost of setting up reference stations for the differential GPS is high and reference stations usually are set up in the spacious or boundless areas having few barriers, such as mountain or suburban areas to collect more complete satellite data.
In the differential GPS, after the server collects and compiles the data of each reference station, a user should acquire the real-time calibration data through a mobile network. However, since the city having larger traffic flow usually is farther away from the location where the reference station is set up, the difference of the satellite calibration data is larger and the vehicular positioning system cannot acquire the calibration value of its environment and only has the limited calibration result. Besides, when the vehicular positioning system acquires the calibration data, the calibration data needs to be downloaded from the server through a 3G network and the cost of the network connection is needed. If there are many users downloading at the same time, the server may be overloaded to cause a service problem.